It has been proposed to clean and convey granular and hygroscopic materials pneumatically for such purposes as sandblasting and bulk material loading. In this respect it was found that a hopper feed bin required a portion of its side wall to have an irregular hyperbolic surface to prevent bridging, packing, clinging and ratholing of finely divided dry materials such as limestone and particularly hygroscopic materials such as salt or sugar, and it is acknowledged that for special purposes such as sandblasting with given materials at known flow rates these systems work well. However, their versatility has been considerably limited and such prior art systems are confined to use for chronic special purpose jobs of limited scope for which they are specially designed in terms of material flow rates, material variety and pneumatic characteristics, thereby significantly limiting the number of applications for a given system. Such special purpose prior art systems include those shown by way of example in U.S. Pat. Nos. 2,827,333, Mar. 18, 1958, S. W. Wallin; 2,446,968, Aug. 10, 1948, G. E. Toner; and 3,876,260, Apr. 8, 1975, R. A. Moss et al.
For example, a system designed for sandblasting on a continuous basis with flow of sand at about 6 tons per hour is not effective in the bulk transport of sugar at 200 tons per hour.
Various problems thus present themselves in achieving a wider range of flow and material capabilities in such pneumatic transport systems. Some problems encountered are (1) achievement of vacuum and compressor systems that are versatile to not only radically different materials such as gypsum, salt, sand and grain, but also can operate continuously at vastly different material flow rates; (2) achievement of off-on batch feed rate capabilities such as needed for loading bags or other limited capacity receptacles; (3) storage for continuous flow of enough materials for feeding a bulk transport pneumatic conveyor line at high flow rates, while operable also for limited flow rates; (4) the ability to adapt to radically different material weights, sizes, moisture contents and other physical attributes such as hygroscopy without equipment change or radically different operating conditions; (5) the basic flow characteristics through a pneumatic conveyor system having ranges from very dense to very sparse packing densities of materials in the flow paths; and (6) efficiency in operation, longevity and maintenance characteristics of a portable transport system of universal capabilities.